Why do we sleep?

A recent study may have an answer to one of the greatest unsolved mysteries in science - what is the purpose of sleep? The work suggests it’s (REAL) about making animals function more efficiently in their environments. (SCIENCE) from the University of California, Los Angeles, conducted a study of the sleep times of a broad range of animals. They discovered much variation. You may think it (POSSIBLE) but some migrating birds can fly non-stop for up to 90 hours. Pythons and bats are among the longest (SLEEP) at over 18 hours a day. Human babies need 16 hours and their health and intellectual (DEVELOP) depend on sleeping properly. Most of us probably feel we need around eight hours sleep to function well. Some people have (DIFFICULT) in getting enough sleep and this may lead to serious health problems.